Manufacture of granular coated products



Au .-12, 1941. F. J. mm; ETAL 2,252,587

MANUFACTURE OF GRANULAR COATED PRODUCTS Original Filed Oct. 12, 1935 INVENTOR. F'QAN K J. TO N E. HAEEY C. MARTIN ATTORNEY.

Patented Aug. 12, 1941 MANUFACTURE OF GRANULAR COATED PRODUCTS Frank J. Tone and Harry 0. Martin, Niagara Falls, N. Y., assignors, by mesne assignments, to The Carborundum Company, Niagara Falls, N. Y., a

corporation of Delaware Continuation of application Serial No. 693,395, October 12, 1933. This application May 13, 1936, Serial No. 79,549

9 Claims.

This invention relates to granular coated products and the method of manufacturing the same; and more specifically to abrasive coated products of a somewhat flexible character, such as belts, discs, and the like.

This application is a continuation of our copending application, Serial No. 693,395, filed ctober 12, 1933.

Abrasive coated flexible discs, which are one of the products for which our invention is particularly well'adapted, have heretofore ordinarily been made by coating a suitable backing, such as vulcanized fibre or vulcanized fibre and cloth, with abrasive granules attached to the backing by means of ,glue. Articles of this type are used fora variety of purposes, such as polishing wood, metal, or lacquered surfaces. For such purposes as these, which might be termed smoothing, a fine grit abrasive would be indicated; but for what might be termed more strictly abrasive purposes, in which the primary object is to remove material rather than to smooth an article, coarse granules would be used. Although our invention is by no means restricted to abrasive articles carrying coarse grits, it is especially well adapted for improving this type of article and lengthening its useful service.

One use to which discs made by our improved process have been satisfactorily applied is in the removal of the excess material applied in making welds; and it has been found, for example, that discs made in accordance with our invention have at least from two to three times the life of the discs made in accordance with the methods heretofore known.

In order to facilitate understanding of the invention we have illustrated it by a number of drawings wherein:

Fig. 1 is a side elevation of a part of a completed article made in accordance with the invention:

Fig. 2 is a plan view of a completed article embodying one modification of the invention:

Fig. 3 is a side elevation of a backing coated with binder, as used in carrying out the invention; and

Fig. 4 is an enlarged sectional view of a coated abrasive grain of the class used in the invention.

Referring to the drawing, the articles comprise a backing'l having abrasive grains 2 attached thereto by a binder 3. The binder of the completed articles comprise the coating 4, which is applied'directly to the backing l (as illustrated is caused to flow to" the backing and unite with the coating 4 when the article is given a suitable heat-treatment as will be fully described hereinafter.

In carrying out one form of ouninvention, we may use an intermediate product which has been found to be valuable in the production of bonded abrasive products, such as wheels or stones. The

method of manufacturing this intermediate product and a method of making bonded abrasives from it are disclosed and claimed in United States Patent No. 2,010,873.

For the purpose of fully explaining our invention, we will now discuss a method of forming this intermediate product which we have found to be particularly well suited for use in our invention.

In making this intermediate product, we first coat abrasive granules with a suitable plasticizing medium, such as a liquid heat-hardenable resin, or other resin solvent. The grain coated with the plasticizing medium is then admixed with a dry powdered heat-hardenable resin, such as a phenolic condensation product in the fusible and soluble condition. By properly adjusting the proportions of the plasticizing medium and powdered resin, as by applying 3 to 4 parts of powdered resin to about 25 to 50 parts of grain which has been wetted by onepart of plasticizing medium it is possible to prepare in this way a product which consists of individually coated abrasive granules which are dry and non-tacky at ordinary temperatures but which are sufficiently cohesive so that upon pressing they can be formed into a shaped article. If, now, the coated granules are passed through a suitable screen, they can be separated into individual grains and spread on a plate, belt or the like in isolated condition.

' If these coated granules are passed through an oven, thetemperature of which is about 350 to 375 F., and are exposed to this heat for a period of about two to ten minutes, while being maintained in an isolated condition such that substantially none of the granules are touching each other, it will be found, that the resin has dissolved, or at least has liquified and merged with the plasticizing medium to form a substantially homogeneous coating ofresin surrounding and encapsulating the individual abrasive grains. Upon cooling, the resin coatings are sufiiciently hard and non-cohesive so that there is no tendency of the grains to agglomerat'e.

In making a coated product with these granules in accordance with one of the methods of this invention, a coating of a suitable liquid heathardenable resin, such as a normally liquid phenolic condensation product formed by reacting a. phenol'and an aldehyde and arresting the such a treatment it will be found that the granules will be attached to the heat-hardened (previously liquid) resin adhesive by reason'of thesolubility cooled the coated grains formed a loose non-co-.

of the coating resin on the rains in the liquid resin adhesive, which causes thetwo resins to mutually fuse and weld whenthe article is heated to cure the bond. At the same time, the coating --for 24 hours at 125F. and then baked for 6 hours resin which was applied to the grain tends to flowto a small extent to form-a mounting for. the coarse granules in the form of a concentration of the resin at the base of each granule.

result of this condition, the grain is especially,

Asa

product resin inithe so-calle'd A stage.

18 parts of bond. This gives a substantially single layer about one grain deep.

The coated grains were prepared by first moistening the surface of 82 parts of grain with 3 parts of a normally liquid phenol-aldehyde condensation product and then dusting on a mixture of 6 parts of pulverized flint and 9 parts of a powdered heat-hardenable phenolic condensation The coated grains were scattered in separated condition on a belt and were then exposed to a temperature of 375 F. for 6 minutes to melt the resin. When herent mass which was sprinkled on the liquid resin :oated.backing.

The disc to which first the liquid resin had been applied and then the coated grain, was next dried at 300?,F. ,This disc had a life of 27 minutes, re-

moving 285 grams of metal, as compared to a life of 9 minutes and 130 grams of metal removed by well attached to the backing, and is very resistthat the grains -are,encapsulatedwith pulverized resin adhesively attached to the individual grains. The other steps followed in producing the coated grains will be the same in all material respectas .those above described. Although coated grain produced byflthis modified methodcan notbe handled 'so satisfactorily from Y a manufacturing standpoint, the abrasive articles themselves produced in accordance with this modification are quite satisfactory The omission of the oven treatment leaves the resin coating on the abrasive grains'in a somewhat fragile condition,;as the resin not firmly attached tothe grains and therefore tends to become dislodged when the grains are applied to the backing. Although considerabl'y more care must be used, for this reason, in carrying out this modified process than in carrying out the preferred process, articles made in accordance therewith are substantially as longlived as those made by the preferred process.

Another process of coating the grain comprises heating a mixture of abrasive grain and normally solid resin in an oven and stirring until the resin melts and coats the grain. The mass of coated grain is then cooled and passed through a crusher whose rolls are spaced somewhat more than the maximum particle size so as to break up the mass into individual coated grains without fracturing the grains.

We will now give a number of specific examples to illustrate our invention, it being understood that the examples are illustrative only and not limitative.

Example 1.The backing selected was a disk of Swedish spring steel 9%" diameter, .015" thick and provided with a hole at its center for the purpose of mounting. -On this disk was applied a coating in the form of a band or ring 2" wide extending from the periphery of the disk toward its center. 5 grams of coating were used, the coating consisting of a mixture of 60 parts of Bakelite" liquid resin No. 1372 and 40 parts of pulverized flint. To the coated portion of the disk were applied 27 grams of coated grain consisting of No. 24 grit fused alumina coated with resin in the proportions of 82 parts of grain to grainwerecoated byfirst moistening the surfaces of the grain with 3' parts of a normally liquid phenol aldehyde condensation product and then dusting the same .with a mixture of 6 parts of pulverized flint and.l0 parts of a powderedheathardenable phenolic condensation product resin in the A 'stage.-. To the disc coatedas above described was appliedthe27grams of coated grain; and the article was then dried for 24 hours at '12 5f F.after which it was baked for 6 hours at 300? F. disc had a life of, 27 minutes and removed 289 ,grams of metal.

v Example'3.A file was made by coating :3. piece of wood 1 square and 12" long with normally liquid phenolic resin andNo. 16 grit fused alumina preparedin accordance with the method described under Example 1. The resin was cured by first drying the article for 14 hours at 150 F. and baking for 12 hours at 250 F.

Example 4.To a disc coated with a mixture of liquid resin and flint as described in Example 1 were applied 27 grams of coated abrasive grain. This coated grain consisted of No. 24 grit fused alumina coated with melted resin in the proportion of 81 parts of grain to 19 parts of bond. The 81 parts of grain were coated by placing the same together with 13 parts of a heat-hardenable phenolic condensation product resin in the A stage and 6 parts of pulverized flint in an oven heated to 375 F. After a sufiicient period of heating to melt the resin, during which period the mixture was stirred, the mass was removed,

from the oven and cooled. The hardened mass was then passed through a crusher whose rolls were spaced sufllciently to permit the largest granules of the No. 24 grit to pass. The coated disc, to which these coated grains had been applied, was next dried for 24 hours at F. and then baked for 6 hours at 300 F. This disc had a life of 21 minutes and removed 196 grams of metal.

The coatings of adhesive and abrasive grains may be applied to the backing in any convenient manner. Where abrasive coated articles are made on backings which are not obtainable in the form of continuous webs, it is convenient to product used for the other.

brush or to spray the liquid onto the backing and then to apply the coated abrasive grains in an excess and remove the excess grain as by inverting the article. Where the backing is obtainable as a web the process may be conveniently carried out in a conventional abrasive coating machine such as is commonly employed in the manufacture of abrasive paper or cloth, usually referred to as sandpaper. As is well-known, in such machines the web of backing. material is continuously passed between a pair of revolving rolls, one of which is partially immersed in a vat of adhesive, thereby coating one side of the backing with the liquid adhesive, and an excessof abrasive grain is fed onto the adhesive coated side of the moving web. The excess abrasive grain is then removed as by passing the coated web down- Xwardly so that unattached grains fall 01f the Web.

We have also applied our process to an improved method of coating which is described and claimed in copending application Serial No. 66,627, filed March 2, 1936, wherein a backing is first coated with a liquid resinous adhesive and partially coated with abrasive grains to cover somewhere about 20% of the surface of the backing and the partially coated web is then additionally coated with a liquid resinous adhesive and resin-coated grains to substantially completely cover the backing and to form clusters of grains about the grains first applied to the backing.

Our method is therefore adapted to be used in any of the methods used for forming thin layers of abrasive grains wherein'a large proportion of the grains are attached directly to a backing member, in distinction to molded articles wherein articles are formed by compacting a mass of grains so as to get a multi-layered article several grains thick. In describing and claiming our invention we have used the expressim "substantially single layer to mean a layer such as is obtainable by coating methods wherein a major proportion of the grains are attached directly to the backing, as distinguished from multi-layered articles such as are obtainable by pressing or otherwise compacting as in a mold, even though the coating of our articles may be more than one gyiin deep in places.

Although, as previously stated, our invention has been' found to be especially suited for the production of flexible discs, it is equally /well adapted to the manufacture of all forms of abrasive coated articles carrying a substantially single layer of abrasive grains, such as abrasive belts or coated fabrics of the nature of sandpaper. As describedin Example 3, we have also found it useful, for example, in the manufacture of files and like articles which may, of course, be made on a more rigid base such as wood or rigid metal.

As is evidenced by the examples, our method is adapted to a number of variations such as the inclusion of inert fillers. It is also, of course, possible to use different types of resin on the grains and on the backing as, for example, a glycerolphthalic anhydride type of resin can be used for either the adhesive or the coating on the grain in combination with a phenolic condensation Obviously, it is also possible to use a solution of a normally solid resin in a suitable solvent, instead of the liquid resin adhesive. These and other modifications are to be understood as coming within the contemplation of our invention, the scope of which is'to'be limited solely by the following claims.

We claim:

1. In the method of making an abrasive article having a coating of abrasive grains, the steps comprising applying a coating of liquid resin to a backing, applying a uniform coating of a solid fusible resin to granular abrasive particles whereby there is obtained a loose distributable mass of abrasive grains to the individual grains of which there is attached a substantial quantity of resin bond, applying a substantially single layer of such coated particles .to the resin coated backing, and heating to set and unite the coatings on the backing and on the particles.

2. The method of making a coated abrasive article which comprises coating abrasive grains with a solid fusible resin so as to form a loose distributable mass of abrasive grains to the in dividual grains of which there is attached a substantial quantity of resin bond, applying a coating of a liquid resinous material to a backing, applying a substantially single layer of the coated grains in a loose condition to the coated backing, and heating the thus coated article to unite the coatings on the backing and on the grains.

3. The method of, making a coated abrasive article which comprises coating abrasive grains with a solid fusible resin so as to form a loose distributable mass of abrasive grains to the individual grains of which there is attached a substantial quantity of resin bond, applying a coating of a liquid resinous material to a backing, applying the coated grains in a loose condition to the coated backing and removing the grains, if any, which are not adhesively retained by the liquid resinous coating, and heating the thus coated article to unite the coatings on the backing and on the grains.

4. The method of making a coated abrasive article which comprises coating abrasive grains with a solid fusible heat-hardenable resin so as to form a loose distributable mass of abrasive grains to the individual grains of which there is attached a substantial quantity of resin bond, applying a coating of a normally-liquid synthetic resin to a backing, applying a substantially single layer of the coated grains in a loose condition to the coated backing, and heating the thus coated article to heat-harden and unite the coatings on the backing and on the grains.

5. The method of making a coated abrasive article which comprises coating abrasive grains with a. solid fusible heat-hardenable resin so as to form a loose distributable mass of abrasive grains to the individual grains of which there is attached a substantial quantity of resinbond, the individualgrains being non-tacky and'dry to the touch, applying a coating of a liquid heat-hardenable resinous material to a backing, applying a substantially single layer of the coated grains in a loose condition to the coated backing, and heating the thus coated article to set and unite the coatings on the backing and on the grains.

6. The method of making a coated abrasive article which comprises coating abrasive grains with a solid fusible resin and a liquid plasticizing agent for the resin, treating the thus coated grains to homogenize the coatings and provide a loose distributable mass of grains individually coated with firm adherent films of resin bond, the individual grains being non-tacky and dry to the touch, applying a coating of a liquid resinous material to a backing, applying a substantially single layer of the coated grains in a loose condition to the coated backing,and heating the thus coated article to unite the coatings on the backing and on the grains.

'7. The method of making a coated abrasive article which comprises coating'abr asive grains with a solid fusible resin and a liquid plasticizing agent for the resin, treating the thus coated grains to homogenize the coatings and provide a loose distributable mass of grains individually coated with firm adherent films of resin bond, the individual grains being non-tacky and dry to the touch, applying a coating of a normally liquid resin to a backing, applying a substantially single layer of the coated grains in a loose condition to the coated backing, and heating the thus coated article to unite the coatings on the backing and on the grains.

8. A coated abrasive article comprising a backing, a substantially single layer of abrasive grains individually encapsulated with films of resin, and a layer of resin adhesively attached to the backing and to the resin coatings on the abrasive grains; a major portion of the abrasive grains being attached directly to the layer of resin on the backing by the fusion and welding of the films of resin on the grains with the layer of resin on the backing.

9. A coated abrasive article comprising a backing and abrasive grains attached thereto by a composite resinous bond, said bond comprising a surface coating spread over and adhesively attachedto a surface of the backing and grain coatings distributed over the surfaces of the individual abrasive grains, said surface coating comprising the heat hardened reaction product of a normally liquid resin and said grain coatings comprising the heat hardened reaction product of a'normally solid resin, said surface coating and said grain coatings being fluxed and welded together so as to form a continuous bond attaching the individual grains to the backing in a substantially single layer.

FRANK J. TONE.

HARRY C. MARTIL 

